1. Field of the Invention
This invention relates to a leakage determination system for an evaporative fuel processing system of an internal combustion engine, for determining whether or not there is a leak in the evaporative fuel processing system which causes a canister to temporarily store evaporative fuel generated from a fuel tank, and supplies the same to an intake system of the engine with proper timing.
2. Description of the Prior Art
Conventionally, a leakage determination system of the above-mentioned kind was proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 9-291854. The evaporative fuel processing system includes a canister, a fuel tank, a charge passage, and a purge passage. The canister is connected to the fuel tank via the charge passage. The charge passage is provided with a pressure sensor that detects pressure within the charge passage (hereinafter referred to as xe2x80x9cthe tank internal pressurexe2x80x9d because the pressure within the charge passage is approximately equal to pressure within the fuel tank in a steady state of the system). In a bypass passage bypassing the charge passage, there is arranged a bypass valve for opening and closing the bypass passage. Further, the canister is connected to an atmosphere passage which is open to the atmosphere, and in the atmosphere passage, there is arranged a vent shut valve for opening and closing the same. In the purge passage, there is arranged a purge control valve for opening and closing the same.
The leakage determination system determines whether or not there is a leak in the evaporative fuel processing system, by carrying out a pressure-reducing mode process and a leakage-checking mode process sequentially as described below. First, in the pressure-reducing mode process, the bypass valve and the purge control valve are opened, and the vent shut valve is closed, whereby the pressure within the evaporative fuel processing system is reduced until the tank internal pressure is lowered to a predetermined negative pressure.
Then, in the leakage-checking mode process, the bypass valve, the purge control valve and the vent shut valve are all closed to maintain the evaporative fuel processing system in a sealed state over a predetermined time period, and in this state, changes in the tank internal pressure are monitored. Through this monitoring, if a change in the tank internal pressure becomes equal to or larger than a predetermined value, it is determined that there is a leak in the system, whereas if the changes in the tank internal pressure are held below the predetermined value, it is determined that there is no leak.
In the above conventional leakage determination system, however, e.g. when the vehicle is jolted with only a small amount of fuel remaining in the fuel tank or when the outside temperature is high, the amount of evaporative fuel within the fuel tank can be increased to raise the tank internal pressure in a short time, which makes it impossible to effect an accurate leakage determination. In short, the leakage-checking mode process is only executed for checking changes in the tank internal pressure within the predetermined time period, and hence if the tank internal pressure is temporarily increased for some reason as mentioned above, it can be erroneously determined that there is a leak, even though there is no leak.
It is an object of the invention to provide a leakage determination system for an evaporative fuel processing system, which, even when pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel in a fuel tank, is capable of performing an accurate leakage determination by eliminating the influence of the temporary rise in the pressure within the evaporative fuel processing system.
To attain the above object, according to a first aspect of the invention, there is provided a leakage determination system for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,
the leakage determination system comprising:
pressure detection means for detecting pressure within the evaporative fuel processing system;
pressure reduction means for reducing the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system;
negative pressure introduction means for introducing the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction by the pressure reduction means; and
leakage determination means for determining whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system by the negative pressure introduction means.
Preferably, the negative pressure introduction means introduces the negative pressure from the intake system at a predetermined constant negative pressure introduction flow rate.
According to this leakage determination system for an evaporative fuel processing system, in a leakage determination process, first, negative pressure is introduced from the intake system into the evaporative fuel processing system, whereby the pressure within the evaporative fuel processing system is reduced to the predetermined negative pressure. Then, after the pressure reduction is terminated, negative pressure is introduced again from the intake system into the evaporative fuel processing system at the predetermined constant negative pressure introduction flow rate, and whether or not there is a leak in the evaporative fuel processing system is determined based on a pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure at the constant flow rate. According to the first aspect of the invention, since the pressure within the evaporative fuel processing system is detected while introducing the negative pressure as described above, the detected pressure represents an offset between an increment of a pressure increased by leakage and a decrement of the same reduced by the introduction of the negative pressure. Therefore, leakage determination for the evaporative fuel processing system can be carried out based on the pressure within the evaporative fuel processing system.
Further, since the pressure within the evaporative fuel processing system is detected while continuously introducing the negative pressure, even when the pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of evaporative fuel generated in the fuel tank, it is possible to carry out leakage determination while reducing the temporary rise in the pressure. Consequently, the influence of the temporary rise in the pressure caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system.
More preferably, the negative pressure introduction means includes pressure re-reduction means for holding the evaporative fuel processing system in a closed state and introducing the negative pressure from the intake system whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, to thereby repeatedly reduce the pressure within the evaporative fuel processing system to a second predetermined negative pressure lower than the predetermined pressure,
the leakage determination system further comprising pressure reduction cycle detection means for detecting a pressure reduction cycle of the pressure reduction performed by the pressure re-reduction means, and
the leakage determination means determining whether or not there is a leak in the evaporative fuel processing system, based on a plurality of pressure reduction cycles detected by the pressure reduction cycle detection means.
According to this preferred embodiment, in the leakage determination process, first, negative pressure is introduced from the intake system, whereby the pressure within the evaporative fuel processing system is reduced to the predetermined negative pressure. After the reduction of the pressure within the evaporative fuel processing system, negative pressure is introduced from the intake system while holding the evaporative fuel processing system in the closed state, whenever the pressure within the evaporative fuel processing system rises to reach the predetermined pressure higher than the predetermined negative pressure, to thereby repeatedly reduce the pressure within the evaporative fuel processing system to the second negative pressure. Then, whether or not there is a leak in the evaporative fuel processing system is determined based on the plurality of pressure reduction cycles detected during the repetition of pressure reduction. If there is a leak in the evaporative fuel processing system, an atmospheric pressure enters the evaporative fuel processing system via the leak. As a result, the rate of increase in the pressure within the evaporative fuel processing system after termination of the pressure reduction becomes faster, and hence the pressure reduction cycle becomes shorter than when there is no leak, so that it is possible to determine from the pressure reduction cycle whether or not there is a leak in the evaporative fuel processing system.
Further, since the pressure within the evaporative fuel processing system is repeatedly reduced, even when the pressure within the evaporative fuel processing system is temporarily increased e.g. due to an increase in the amount of generation of evaporative fuel in the fuel tank, it is possible to reduce the temporary rise in the pressure whenever it occurs, and detect a pressure reduction cycle subsequent thereto. Moreover, since whether or not there is a leak in the evaporative fuel processing system is determined based on the plurality of pressure reduction cycles detected during the repetition of pressure re-reduction, even when a temporary rise in the pressure has caused a variation in the pressure reduction cycle, it is possible to assess the plurality of pressure reduction cycles as a whole, thereby compensating for the variation in the pressure reduction cycle. Thus, the influence of the temporary rise in the pressure caused by other factors than leakage on the leakage determination can be eliminated, which enables accurate determination of whether or not there is a leak in the evaporative fuel processing system.
To attain the above object, according to a second aspect of the invention, there is provided a leakage determination method for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine,
the leakage determination method comprising:
a pressure detection step of detecting pressure within the evaporative fuel processing system;
a pressure reduction step of reducing the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system;
a negative pressure introduction step of introducing the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction at the pressure reduction step; and
a leakage determination step of determining whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system.
Preferably, at the negative pressure introduction step, the negative pressure from the intake system is introduced at a predetermined constant negative pressure introduction flow rate.
More preferably, in the leakage determination method according to the second aspect of the invention, at the negative pressure introduction step, the negative pressure is introduced from the intake system while holding the evaporative fuel processing system in a closed state whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, whereby the pressure within the evaporative fuel processing system is repeatedly reduced to a second predetermined negative pressure lower than the predetermined pressure,
the leakage determination method further comprising a pressure reduction cycle detection step of detecting a pressure reduction cycle of the pressure reduction at the negative pressure introduction step, and
the leakage determination step includes determining whether or not there is a leak in the evaporative fuel processing system based on a plurality of detected pressure reduction cycles.
To attain the above object, according to a third aspect of the invention, there is provided a recording medium storing a leakage determination control program for causing a computer to carry out leakage determination for an evaporative fuel processing system that causes a canister to absorb evaporative fuel generated from a fuel tank and supplies the evaporative fuel absorbed in the canister to an intake system of an internal combustion engine.
The recording medium is characterized in that the leakage determination control program causes the computer to detect pressure within the evaporative fuel processing system, reduce the pressure within the evaporative fuel processing system until the detected pressure within the evaporative fuel processing system becomes equal to a predetermined negative pressure, by introducing negative pressure from the intake system, introduce the negative pressure from the intake system into the evaporative fuel processing system under predetermined conditions after the pressure reduction to the predetermined negative pressure, and determine whether or not there is a leak in the evaporative fuel processing system, based on a state of the pressure within the evaporative fuel processing system, which has been detected during the introduction of the negative pressure from the intake system.
Preferably, the leakage determination control program causes the negative pressure to be introduced from the intake system at a predetermined constant negative pressure introduction flow rate, after the pressure reduction to the predetermined negative pressure.
Also preferably, the leakage determination control program causes the negative pressure to be introduced while causing the evaporative fuel processing system to be held in a closed state, after the pressure reduction to the predetermined negative pressure, whenever the pressure within the evaporative fuel processing system rises to a predetermined pressure higher than the predetermined negative pressure, thereby repeatedly reducing the pressure within the evaporative fuel processing system to a second predetermined negative pressure lower than the predetermined pressure, detecting a cycle of the pressure reduction, and determining whether or not there is a leak in the evaporative fuel processing system, based on a plurality of detected pressure reduction cycles.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.